I've got a page with two collapsible regions (both static content). In one of the regions, I've got a sub-region with a form, in the other, there are two sub-regions which are interactive grids.
When the page loads, the "Abo(s) erstellen" region is expanded and the "Abo(s) bearbeiten" region is collapsed. When the user collpases the expanded region or expands the collapsed region via clicking the respective button, the other region should change automatically.
I've tried to test this with a button and a dynamic action that gets fired when the button is clicked:

This doesn't show the content of ths region, it just switches the button from "+" to "+". Furthermore, I wonder how to implement this without a button: Event listener in html header?! What kind of event would I have to choose in this case?
Any help is highly appreciated